Method of Enhancing an Aromatization Catalyst

ABSTRACT

A hydrocarbon aromatization process comprising adding a nitrogenate, an oxygenate, or both to a hydrocarbon stream to produce an enhanced hydrocarbon stream, and contacting the enhanced hydrocarbon stream with an aromatization catalyst, thereby producing an aromatization reactor effluent comprising aromatic hydrocarbons, wherein the catalyst comprises a non-acidic zeolite support, a group VIII metal, and one or more halides. Also disclosed is a hydrocarbon aromatization process comprising monitoring the presence of an oxygenate, a nitrogenate, or both in an aromatization reactor, monitoring at least one process parameter that indicates the activity of the aromatization catalyst, modifying the amount of the oxygenate, the nitrogenate, or both in the aromatization reactor, thereby affecting the parameter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional Application of U.S. patent application Ser. No.11/780,693 filed Jul. 20, 2007, published as U.S. 2008-0027255 A1, andentitled “Method of Enhancing an Aromatization Catalyst,” which claimspriority to U.S. Provisional Patent Application Ser. No. 60/820,748filed Jul. 28, 2006 by Blessing et al. and entitled “Method ofActivating an Aromatization Catalyst”, each of which is incorporatedherein by reference as if reproduced in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

The disclosure generally relates to aromatization of hydrocarbons withan aromatization catalyst. Specifically, the disclosure relates to amethod for activating and/or enhancing an aromatization catalyst by theaddition of an oxygenate, a nitrogenate, or both.

The catalytic conversion of hydrocarbons into aromatic compounds,referred to as aromatization or reforming, is an important industrialprocess. The aromatization reactions may include dehydrogenation,isomerization, and hydrocracking the hydrocarbons, each of whichproduces specific aromatic compounds. These reactions are generallyconducted in one or more aromatization reactors containing anaromatization catalyst. The catalyst may increase the reaction rates,production of desired aromatics, and/or the throughput rates for thedesired aromatic compounds. Given their commercial importance, anongoing need exists for improved methods and systems related toaromatization processes and catalysts.

SUMMARY

In one aspect, the disclosure includes a hydrocarbon aromatizationprocess comprising adding a nitrogenate, an oxygenate, or both to ahydrocarbon stream to produce an enhanced hydrocarbon stream, andcontacting the enhanced hydrocarbon stream with an aromatizationcatalyst, thereby producing an aromatization reactor effluent comprisingaromatic hydrocarbons, wherein the catalyst comprises a non-acidiczeolite support, a group VIII metal, and one or more halides.

In another aspect, the disclosure includes a hydrocarbon aromatizationprocess comprising adding a nitrogenate, an oxygenate, or both to ahydrocarbon stream to produce an enhanced hydrocarbon stream, to ahydrogen recycle stream to produce an enhanced recycle stream, or toboth, contacting the enhanced hydrocarbon stream, enhanced recyclestream, or both with an aromatization catalyst in an aromatizationreactor to produce an aromatization reactor effluent comprising aromatichydrocarbons, and controlling the addition of the nitrogenate, theoxygenate, or both to the enhanced hydrocarbon stream, the enhancedrecycle stream, or both in order to maintain one or more processparameters within a desired range.

In yet another aspect, the disclosure includes a hydrocarbonaromatization process comprising monitoring the presence of anoxygenate, a nitrogenate, or both in an aromatization reactor,monitoring at least one process parameter that indicates the activity ofthe aromatization catalyst, modifying the amount of the oxygenate, thenitrogenate, or both in the aromatization reactor, thereby affecting theparameter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram showing one embodiment of anaromatization system;

FIG. 2A illustrates one manner for adding the oxygenate and/or thenitrogenate to the aromatization catalyst.

FIG. 2B illustrates another manner for adding the oxygenate and/or thenitrogenate to the aromatization catalyst.

FIG. 2C illustrates another manner for adding the oxygenate and/or thenitrogenate to the aromatization catalyst.

FIG. 2D illustrates another manner for adding the oxygenate and/or thenitrogenate to the aromatization catalyst.

FIG. 3A is a chart illustrating the relationship between water contentand time on stream for an aromatization catalyst;

FIG. 3B is a chart illustrating the relationship between T_(eq) and timeon stream for an aromatization catalyst;

FIG. 4 is a chart illustrating the relationship between yield-adjustedtemperature and time on stream for an aromatization catalyst;

FIG. 5 is another chart illustrating the relationship betweenyield-adjusted temperature and time on stream for an aromatizationcatalyst;

FIG. 6 is a chart illustrating the relationship between theyield-adjusted temperature (T_(yld)) and time on stream for anaromatization catalyst;

FIG. 7 is another chart illustrating the relationship between theyield-adjusted temperature (T_(yld)) and time on stream for anaromatization catalyst;

FIG. 8A is a chart illustrating the relationship between feed rate andtime on stream for an aromatization catalyst;

FIG. 8B is a chart illustrating the relationship between benzene yieldand time on stream for an aromatization catalyst;

FIG. 8C is a chart illustrating the relationship between benzeneconversion, endothermic activity, and time on stream for anaromatization catalyst;

FIG. 8D is a chart illustrating the relationship between T_(eq) and timeon stream for an aromatization catalyst;

FIG. 9 is a chart illustrating the relationship between yield-adjustedtemperature and time on stream for an aromatization catalyst;

FIG. 10 is a chart illustrating the relationship between aromaticproduction and time on stream for an aromatization catalyst;

FIG. 11 is a chart illustrating the relationship between welltemperature and time on stream for an aromatization catalyst.

DETAILED DESCRIPTION

Novel methods and systems for aromatizing hydrocarbons and/oractivating, preserving, and/or increasing the productivity of anaromatization catalyst are disclosed herein. Generally, it has beenthought that water and impurities that can be converted to water aredetrimental to aromatization catalysts, causing sintering of theplatinum, thereby damaging the catalyst. Thus, the conventional wisdomis that water, oxygenates, or nitrogenates should be rigorously purgedfrom the aromatization system. For example, it has generally beenconsidered advantageous to substantially reduce or eliminate thepresence of water and oxygen in the hydrocarbon feed to thearomatization system and/or a hydrogen recycle stream within thearomatization system when using the catalysts described herein.Specifically, water levels as low as a half part per million by volume(0.5 ppmv) in the feed and the hydrogen recycle have been desirable.Such generally accepted wisdom is evidenced by the presence ofhydrotreaters and dryers in the feed stream and dryers in the hydrogenrecycle stream of conventional aromatization processes. Contrary to suchcommonly accepted wisdom, the inventors have found that some water isbeneficial in activating, preserving, and/or increasing the productivityof certain types of aromatization catalysts. Specifically, an oxygenate,a nitrogenate, or mixtures thereof may be inserted into thearomatization system at various times, in various locations, and invarious manners, thereby causing a specific amount of water and/orammonia to be present in one or more aromatization reactors during thearomatization process. In an embodiment, the presence of the specificamount of water and/or ammonia in the aromatization reactor activates orenhances the aromatization catalyst.

FIG. 1 illustrates one embodiment of a catalytic reactor system 100suitable for use in an aromatization system and process as describedherein. In the embodiment shown in FIG. 1, the catalytic reactor system100 comprises four aromatization reactors in series: reactors 10, 20,30, and 40. However, the catalytic reactor system 100 may comprise anysuitable number and configuration of aromatization reactors, for exampleone, two, three, five, six, or more reactors in series or in parallel.As aromatization reactions are highly endothermic, large temperaturedrops occur across the reactors 10, 20, 30, and 40. Therefore, eachreactor 10, 20, 30, and 40 in the series may comprise a correspondingfurnace 11, 21, 31, and 41, respectively, for reheating components backto a desired temperature for maintaining a desired reaction rate.Alternatively, one or more reactors 10, 20, 30, and 40 may share acommon furnace where practical. All of the reactors 10, 20, 30, and 40,furnaces 11, 21, 31, and 41, and associated piping may be referred toherein as the reaction zone.

In FIG. 1, the hydrocarbon feed 101 is combined with recycle stream 119to form combined feed stream 102, which is fed into purification process80. The purification process 80 employs known processes to purify thehydrocarbon feed, which may include fractionation and/or treating thehydrocarbon feed. As used herein, the term “Fractionation” includesremoving heavy (e.g., C₉ ⁺) hydrocarbons and/or light (e.g., C₅ ⁻)hydrocarbons. As used herein, the term “Treating” and “Removing” referinterchangeably to removing impurities, such as oxygenates, sulfur,and/or metals, from the hydrocarbon feed. The resulting purified feed103 may be combined with a dry hydrogen recycle 116 to produce hydrogenrich purified feed 104, which may then be combined with the oxygenateand/or the nitrogenate 105 to produce a reactor feed stream 106.Oxygenate and/or nitrogenate may be fed to the reactor system 100 at oneor more locations in addition to stream 105 or as an alternative tostream 105, as will be described in more detail herein.

The reactor feed stream 106 is pre-heated in a first furnace 11, whichheats the hydrocarbons to a desired temperature, thereby producing afirst reactor feed 107. First reactor feed 107 is fed into reactor 10,where the hydrocarbons are contacted with an aromatization catalystunder suitable reaction conditions (e.g., temperature and pressure) thataromatize one or more components in the feed, thereby increasing thearomatics content thereof. A first reactor effluent 108 comprisingaromatics, unreacted feed, and other hydrocarbon compounds or byproductsare recovered from the first reactor 10.

The first reactor effluent 108 is then pre-heated in the second furnace21, which heats the hydrocarbons to a desired temperature, therebyproducing a second reactor feed 109. Second reactor feed 109 is then fedinto reactor 20, where the hydrocarbons are contacted with anaromatization catalyst under suitable reaction conditions foraromatizing one or more components in the feed to increase the aromaticscontent thereof. A second reactor effluent 110 comprising aromatics,unreacted feed, and other hydrocarbon compounds or byproducts arerecovered from the second reactor 20.

The second reactor effluent 110 is then pre-heated in the third furnace31, which heats the hydrocarbons to a desired temperature, therebyproducing a third reactor feed 111. Third reactor feed 111 is then fedinto reactor 30, where the hydrocarbons are contacted with anaromatization catalyst under suitable reaction conditions foraromatizing one or more components in the feed to increase the aromaticscontent thereof. A third reactor effluent 112 comprising aromatics,unreacted feed, and other hydrocarbon compounds or byproducts isrecovered from the third reactor 30.

The third reactor effluent 112 is then pre-heated in the fourth furnace41, which heats the hydrocarbons to a desired temperature, therebyproducing a fourth reactor feed 113. Fourth reactor feed 113 is then fedinto reactor 40, where the hydrocarbons are contacted with anaromatization catalyst under suitable reaction conditions foraromatizing one or more components in the feed to increase the aromaticscontent thereof. A fourth reactor effluent 114 comprising aromatics,unreacted feed, and other hydrocarbon compounds or byproducts isrecovered from the fourth reactor 40.

The fourth reactor effluent 114 is then fed into a hydrogen separationprocess 50 that uses a number of known processes to separate a hydrogenrecycle 115 from a reformate 117. The reformate 117 comprises thearomatization reaction products from reactors 10, 20, 30, and 40 (e.g.,aromatic and non-aromatic compounds) in addition to any unreacted feedand other hydrocarbon compounds or byproducts. The hydrogen recycle 115may be dried in a dryer 60, thereby forming dry hydrogen recycle 116,which may then be recycled into the purified feed 103. The reformate 117goes to a purification-extraction process 70, which separates theraffinate recycle 119 and reactor byproducts (not shown) from thearomatics 118. The hydrogen separation processes 50 and thepurification-extraction processes 70 are well known in the art and aredescribed in numerous patents, including U.S. Pat. No. 5,401,386 toMorrison et al. entitled “Reforming Process for Producing High-PurityBenzene”, U.S. Pat. No. 5,877,367 to Witte entitled “DehydrocyclizationProcess with Downstream Dimethylbenzene Removal”, and U.S. Pat. No.6,004,452 to Ash et al. entitled “Process for Converting HydrocarbonFeed to High Purity Benzene and High Purity Paraxylene”, each of whichis incorporated herein by reference as if reproduced in its entirety.The raffinate recycle 119 is then recycled into the feed 101 and thearomatics 118 are sold or otherwise used as desired. For the sake ofsimplicity, FIG. 1 does not illustrate the byproduct streams that areremoved from the catalytic reactor system 100 at various pointsthroughout the system. However, persons of ordinary skill in the art areaware of the composition and location of such byproduct streams. Also,while FIG. 1 shows the oxygenate and/or nitrogenate 105 being added tohydrogen rich purified feed 104, persons of ordinary skill in the artwill appreciate that the oxygenate and/or nitrogenate may be added toany of process streams 101, 102, 103, 104, 106, 107, 108, 109, 110, 111,112, 113, 114, 115, 116, 117, 119, or various combinations thereof.

In various embodiments, the catalytic reactor system described hereinmay comprise a fixed catalyst bed system, a moving catalyst bed system,a fluidized catalyst bed system, or combinations thereof. Such reactorsystems may be batch or continuous. In an embodiment, the catalyticreactor system is a fixed bed system comprising one or more fixed bedreactors. In a fixed bed system, the feed may be preheated in furnacetubes and passed into at least one reactor that contains a fixed bed ofthe catalyst. The flow of the feed can be upward, downward, or radiallythrough the reactor. In various embodiments, the catalytic reactorsystem described herein may be operated as an adiabatic catalyticreactor system or an isothermal catalytic reactor system. As usedherein, the term “catalytic reactor” and “reactor” refer interchangeablyto the reactor vessel, reactor internals, and associated processingequipment, including but not limited to the catalyst, inert packingmaterials, scallops, flow distributors, center pipes, reactor ports,catalyst transfer and distribution system, furnaces and other heatingdevices, heat transfer equipment, and piping.

In an embodiment, the catalytic reactor system is an aromatizationreactor system comprising at least one aromatization reactor and itscorresponding processing equipment. As used herein, the terms“aromatization,” “aromatizing,” and “reforming” refer to the treatmentof a hydrocarbon feed to provide an aromatics enriched product, which inone embodiment is a product whose aromatics content is greater than thatof the feed. Typically, one or more components of the feed undergo oneor more reforming reactions to produce aromatics. Some of thehydrocarbon reactions that occur during the aromatization operationinclude the dehydrogenation of cyclohexanes to aromatics,dehydroisomerization of alkylcyclopentanes to aromatics,dehydrocyclization of acyclic hydrocarbons to aromatics, or combinationsthereof. A number of other reactions also occur, including thedealkylation of alkylbenzenes, isomerization of paraffins, hydrocrackingreactions that produce light gaseous hydrocarbons, e.g., methane,ethane, propane and butane, or combinations thereof.

The aromatization reaction occurs under process conditions thatthermodynamically favor the dehydrocyclization reaction and limitundesirable hydrocracking reactions. The pressures may be from about 0pounds per square inch gauge (psig) to about 500 psig, alternativelyfrom about 25 psig to about 300 psig. The molar ratio ofhydrogen-to-hydrocarbons may be from about 0.1:1 to about 20:1,alternatively from about 1:1 to about 6:1. The operating temperaturesinclude reactor inlet temperatures from about 700° F. to about 1050° F.,alternatively from about 900° F. to about 1000° F. Finally, the liquidhourly space velocity (LHSV) for the hydrocarbon feed over thearomatization catalyst may be from about 0.1 to about 10 hr⁻¹,alternatively from about 0.5 to about 2.5 hr⁻¹.

The composition of the feed is a consideration when designing catalyticaromatization systems. In an embodiment, the hydrocarbon feed comprisesnon-aromatic hydrocarbons containing at least six carbon atoms. The feedto the aromatization system is a mixture of hydrocarbons comprising C₆to C₈ hydrocarbons containing up to about 10 wt % and alternatively upto about 15 wt % of C₅ and lighter hydrocarbons (C₅ ⁻) and containing upto about 10 wt % of C₉ and heavier hydrocarbons (C₉ ⁺). Such low levelsof C₉+ and C₅ ⁻ hydrocarbons maximize the yield of high value aromatics.In some embodiments, an optimal hydrocarbon feed maximizes thepercentage of C₆ hydrocarbons. Such a feed can be achieved by separatinga hydrocarbon feedstock such as a full range naphtha into a lighthydrocarbon feed fraction and a heavy hydrocarbon feed fraction, andusing the light fraction.

In another embodiment, the feed is a naphtha feed. The naphtha feed maybe a light hydrocarbon, with a boiling range of about 70° F. to about450° F. The naphtha feed may contain aliphatic, naphthenic, orparaffinic hydrocarbons. These aliphatic and naphthenic hydrocarbons areconverted, at least in part, into aromatics in the aromatization reactorsystem. While catalytic aromatization typically refers to the conversionof naphtha, other feedstocks can be treated as well to provide anaromatics enriched product. Therefore, while the conversion of naphthais one embodiment, the present disclosure can be useful for activatingcatalysts for the conversion or aromatization of a variety of feedstockssuch as paraffin hydrocarbons, olefin hydrocarbons, acetylenehydrocarbons, cyclic paraffin hydrocarbons, cyclic olefin hydrocarbons,and mixtures thereof, and particularly saturated hydrocarbons.

In an embodiment, the feedstock is substantially free of sulfur, metals,and other known poisons for aromatization catalysts, and is initiallysubstantially free of oxygenates and nitrogenates. If present, suchpoisons can be removed using methods known to those skilled in the art.In some embodiments, the feed can be purified by first usingconventional hydrofining techniques, then using sorbents to remove theremaining poisons. Such hydrofining techniques and sorbents are includedin the purification process described below.

In an embodiment, an oxygenate, a nitrogenate, or both may be added toone or more process streams and/or components in the catalytic reactorsystem 100. As used herein, the term “oxygenate” refers to water or anychemical compound that forms water under catalytic aromatizationconditions, such as oxygen, oxygen-containing compounds, hydrogenperoxide, alcohols, ketones, esters, ethers, carbon dioxide, aldehydes,carboxylic acids, lactones, ozone, carbon monoxide or combinationsthereof. In one embodiment, water and/or steam is used as the oxygenate.In another embodiment, oxygen may be used as the oxygenate, wherein suchoxygen converts to water in situ within one or more aromatizationreactors under typical aromatization conditions or within one or morehydrofining catalyst or sorbent beds under normal hydrofiningconditions. Furthermore, the oxygenate may be any alcohol-containingcompound. Specific examples of suitable alcohol-containing compounds aremethanol, ethanol, propanol, isopropanol, butanol, t-butanol, pentanol,amyl alcohol, hexanol, cyclohexanol, phenol, or combinations thereof.

As used herein, the term “nitrogenate” refers to ammonia or any chemicalcompound that forms ammonia under catalytic aromatization conditionssuch as nitrogen, nitrogen-containing compounds, alkyl amines, aromaticamines, pyridines, pyridazines, pyrimidines, pyrazines, triazines,heterocyclic N-oxides, pyrroles, pyrazoles, imadazoles, triazoles,nitriles, amides, ureas, imides, nitro compounds, nitroso compounds, orcombinations thereof. While not wanting to be limited by theory, it isbelieved that the ammonia will improve catalyst activity in much thesame way as the water. Additionally, all the methods of addition andcontrol for oxygenates described herein can also be fully appliedadditionally or alternatively to the methods of addition and control fornitrogenates.

Persons of ordinary skill in the art will appreciate that any of theoxygenates, nitrogenates, or mixtures thereof described herein may beused alone, in combination, or further combined to produce othersuitable oxygenates or nitrogenates. In some embodiments, the oxygenateand nitrogenate may be contained within the same bifunctional compound.The oxygenate and/or nitrogenate may be added in any suitable physicalphase such as a gas, liquid, or combinations thereof. The oxygenateand/or nitrogenate may be added to one or more process streams and/orcomponents via any suitable means for their addition, for example apump, injector, sparger, bubbler, or the like. The oxygenate and/ornitrogenate may be introduced as a blend with a carrier. In someembodiments, the carrier is hydrogen, a hydrocarbon, nitrogen, a noblegas, or mixtures thereof. In a preferred embodiment, the carrier ishydrogen.

The oxygenate and/or nitrogenate may be added at various locationswithin the aromatization system described herein. For example, theoxygenate and/or nitrogenate may be added to one or more process streamsin the catalytic reactor system 100, to one or more equipment componentsor vessels of the catalytic reactor system 100, or combinations thereof.In an embodiment, the oxygenate and/or nitrogenate may be added at oneor more locations within a reaction zone defined by the reactor system100, wherein the reaction zone comprises process flow lines, equipment,and/or vessels wherein reactants are undergoing an aromatizationreaction. In one embodiment, the oxygenate and/or nitrogenate is addedbetween the purification process 80 and the first furnace 11, eitherbefore the addition of the dry hydrogen recycle 116, or after theaddition of the dry hydrogen recycle 116 as depicted in FIG. 1.Alternatively, the oxygenate and/or nitrogenate may be added within thepurification process 80. However, it is also contemplated that theoxygenate and/or nitrogenate can be added at various other locationswithin the catalytic reactor system 100. For example, the oxygenateand/or nitrogenate can be added to the feed 101, the combined feed 102,the first reactor feed 107, the first reactor effluent 108, the secondreactor feed 109, the second reactor effluent 110, the third reactorfeed 111, the third reactor effluent 112, the fourth reactor feed 113,or combinations thereof. In addition, the oxygenate and/or nitrogenatecould be added to the fourth reactor effluent 114, the hydrogen recycle115, the dry hydrogen recycle 116, the reformate 117, the raffinaterecycle 119, or combinations thereof. Furthermore, the oxygenate and/ornitrogenate can be added to any combination of the aforementionedstreams, directly to any of the reactors 10, 20, 30, or 40, directly tothe furnaces 11, 21, 31, 41, or combinations thereof. Likewise, theoxygenate and/or nitrogenate can be added directly to any other processequipment or component of the catalytic reactor system 100 such as apump, value, port, tee, manifold, etc. Finally, it is possible to addthe oxygenate and/or nitrogenate to any process equipment or componentupstream of the catalytic reactor system 100 such as a tank, pump,value, port, tee, manifold, etc. that supplies the feed 101 to thecatalytic reactor system.

The oxygenate and/or nitrogenate may be added to the aromatizationprocess at any time during the service life of the aromatizationcatalyst. As used herein, the term “time” may refer to the point in theservice life of the aromatization catalyst at which the oxygenate and/ornitrogenate is added to the catalyst. For example, the oxygenate and/ornitrogenate may be added at the beginning of the life of thearomatization catalyst, e.g. when or soon after a new batch of catalystis brought online. Alternatively, the oxygenate and/or nitrogenate maybe added to the catalyst close to or at the end of the catalyst run. Theend of the catalyst run may be determined using any of the methodsdescribed herein and known in the art, such as a time-based lifetimesuch as 1,000 days online, or a temperature-based lifetime exceeds adefined value, e.g., 1000° F., which often is based upon processlimitations such as reactor metallurgy. Further, the oxygenate and/ornitrogenate may be added continuously during the lifetime of thecatalyst, e.g. from when the catalyst is brought online to when thecatalyst is taken offline. Finally, the oxygenate and/or nitrogenate maybe added to the aromatization catalyst at any combination of thesetimes, such as at the beginning and at the end of a catalyst lifetime,but not continuously.

In addition, the oxygenate and/or nitrogenate may be added to thearomatization process in any suitable manner. As used herein, the term“manner” may refer to the addition profile of the oxygenate and/ornitrogenate, for example how the addition of the oxygenate and/ornitrogenate to the catalyst changes over time. FIGS. 2A, 2B, 2C, and 2Dillustrate four manners in which the oxygenate and/or nitrogenate may beadded to the aromatization catalyst. Specifically, FIG. 2A illustratesthe case where the oxygenate and/or nitrogenate is added as aconstant-level step increase. Such would be the case when the oxygenateand/or nitrogenate is increased from about 2 ppmv to about 10 ppmvduring the catalyst life. The step may be an increase or a decrease inoxygenate and/or nitrogenate levels. FIG. 2B illustrates the case wherethe amount of oxygenate and/or nitrogenate is increased a step changeand then at a steady rate (e.g., constant slope) over time. Such wouldbe the case when the oxygenate and/or nitrogenate is increased from 0 to2 ppmv at a start point, and thereafter at a rate of 0.2 ppmv/day. Insuch an embodiment, the increase in oxygenate and/or nitrogenate at asteady rate may be preceded by an initial step, as shown in FIG. 2B, ormay lack the initial step (i.e., may start at 0 ppmv). FIG. 2Cillustrates the case where the amount of oxygenate and/or nitrogenate isdecreased at a steady rate over time. Such would be the case when theoxygenate and/or nitrogenate is decreased at a rate of 0.2 ppmv/day. Insuch an embodiment, the increase in oxygenate and/or nitrogenate may bepreceded by an initial step, as shown in FIG. 2C, or may lack theinitial step, such as when it is desirable to reduce the oxygenateand/or nitrogenate levels. FIG. 2D illustrates the case where theoxygenate and/or nitrogenate is added as a pulse. Such would be the casewhen the oxygenate and/or nitrogenate is increased from about 2 ppmv toabout 10 ppmv for two days, then returned to 2 ppmv. The oxygenateand/or nitrogenate may be added in multiple pulses, if desired.

While the addition profiles illustrated in FIGS. 2A, 2B, 2C, and 2D areshown near the end of the catalyst life, those addition profiles may beimplemented at any point during the catalyst life. Specifically, theaddition profiles illustrated in FIGS. 2A, 2B, 2C, and 2D may beimplemented at the beginning of the catalyst life, shortly after thebeginning of the catalyst life, at any point during the catalyst life,or at the end of the catalyst life. In addition, the oxygenate and/ornitrogenate may be added in any combinations of the above manners, suchas two pulses followed by an increasing amount of oxygenate and/ornitrogenate at a constant rate.

The addition of the oxygenate and/or nitrogenate to the aromatizationprocess may be a function of any of the aforementioned locations, times,and/or manners. For example, the sole consideration in adding theoxygenate and/or nitrogenate to the aromatization process may be thetime when the oxygenate and/or nitrogenate is added to the aromatizationprocess, the location where the oxygenate and/or nitrogenate is added tothe aromatization process, or the manner in which the oxygenate and/ornitrogenate is added to the aromatization process. However, theoxygenate and/or nitrogenate will typically be added to thearomatization process using a combination of these considerations. Forexample, the oxygenate and/or nitrogenate may be added in a combinationof times and locations irrespective of manner, times and mannersirrespective of locations, or locations and manners irrespective oftimes. Alternatively, the time, location, and manner may all beconsiderations when adding the oxygenate and/or nitrogenate to thearomatization system.

In an embodiment, the addition of oxygenate and/or nitrogenate to thecatalytic reactor system 100 as described herein functions to activatethe aromatization catalyst, wherein such catalyst might otherwise beinactive or display insufficient activity in the absence of the additionof oxygenate. For example, certain types of aromatization catalysts suchas L-zeolite supported platinum containing one or more halogens such asF and/or Cl may not activate or may have inadequate activity where thefeed to the reactors, e.g., 10, 20, 30, 40, is substantially free ofoxygenate, for example containing less than about 1 ppmv total oxygenateand/or nitrogenate, alternatively less than about 0.5 ppmv totaloxygenate and/or nitrogenate in the hydrogen recycle stream 115. Thus,in some embodiments, the addition of oxygenate and/or nitrogenate asdescribed herein may serve to activate and maintain such catalystsresulting in desirable conversion rates of reactants to aromatics aswell as other benefits such as improved fouling characteristics andcatalyst operating life as described herein. Thus, catalyst activity oractivation may be controlled with addition or removal of an oxygenateand/or nitrogenate. In an additional embodiment, a nitrogenate maysimilarly be added to the catalytic reactor system 100 and function toactivate the aromatization catalyst, wherein such catalyst mightotherwise be inactive or display insufficient activity in the absence ofthe addition of nitrogenate.

In an embodiment, the addition of the oxygenate and/or nitrogenateincreases the useful life of the aromatization catalyst. As used herein,the term “useful life” may refer to the time between when thearomatization catalyst is placed in service, and when one or moreparameters indicate that the aromatization catalyst should be removedfrom service (e.g., reaching a T_(eq) maximum or limit). While the time,location, and manner of oxygenate and/or nitrogenate addition can affectthe useful life of the aromatization catalyst, in embodiments theaddition of the oxygenate and/or nitrogenate can increase the usefullife of the catalyst by at least about 5 percent, at least about 15percent, or at least about 25 percent. In other embodiments, theaddition of the oxygenate and/or nitrogenate can increase the usefullife of the catalyst by at least about 50 days, at least about 150 days,or at least about 250 days.

In an embodiment, the addition of the oxygenate and/or nitrogenateincreases the selectivity and/or productivity of the aromatizationcatalyst. As used herein, “selectivity” may refer to the ratio ofaromatic products produced by the aromatization catalyst for a given setof reagents. As used herein, “productivity” may refer to the amount ofaromatic products produced by the aromatization catalyst per unit offeed and unit time. When the oxygenate and/or nitrogenate is added tothe aromatization catalyst, an increased amount of one or more aromaticcompounds may be produced. Specifically, the addition of the oxygenateand/or nitrogenate to the aromatization catalyst may increase the amountof aromatics in the effluent by at least about 20 percent, at leastabout 10 percent, at least about 5 percent, or at least about 1 percentover pre-addition levels. Also, the addition of the oxygenate and/ornitrogenate to the aromatization catalyst may increase the catalystselectivity to desirable aromatics, such as benzene. In an embodiment,the addition of the oxygenate and/or nitrogenate to the aromatizationcatalyst may increase the catalyst selectivity to desirable aromatics byat least about 20 percent, at least about 10 percent, at least about 5percent, or at least about 1 percent over pre-addition levels. In aspecific example, benzene production may be increased from about 40weight percent to about 48 weight percent of the effluent, withoutdecreasing the production of any of the other aromatics. Such wouldindicate an increase in catalyst production and selectivity. In someembodiments, such effects may be independent of each other such as whenbenzene production is increased with no increase in overall aromaticproduction.

In an embodiment, the methods described herein may yield alternativebenefits. For example, if the aromatic production level is maintained ata specified level, then the reactors may be operated at lowertemperatures, which results in a longer catalyst life. Alternatively, ifthe reactor temperatures are maintained at a specified level, then thespace velocity within the reactors may be increased, which producesadditional amounts of aromatic products. Finally, the methods describedherein may yield additional advantages not specifically discussedherein.

In an embodiment, the effects of the addition of the oxygenate and/ornitrogenate are fast and reversible. For example, when the oxygenateand/or nitrogenate is added to the aromatization catalyst, the oxygenateand/or nitrogenate begins to affect the aromatization catalyst (e.g.,increases activity) within about 100 hours, within about 50 hours,within about 10 hours, or within about 1 hour. Similarly, once theoxygenate and/or nitrogenate is removed from the aromatization catalyst,the aromatization catalyst may revert to the catalyst activity,aromatics yield, or aromatics selectivity seen prior to the addition ofthe oxygenate and/or nitrogenate within about 500 hours, within about100 hours, within about 50 hours, or within about 10 hours.

In an embodiment, the existing oxygenate and/or nitrogenate content of astream to which the oxygenate and/or nitrogenate is to be added ismeasured and/or adjusted prior to addition of the oxygenate and/ornitrogenate. For example and with reference to FIG. 1, one or more feedstreams such as hydrocarbon feed 101, recycle stream 119, combined feedstream 102, hydrogen recycle 116, or combinations thereof may bemeasured for oxygenate and/or nitrogenate content and the oxygenateand/or nitrogenate content thereof adjusted prior to the addition of theoxygenate and/or nitrogenate. Likewise, the same streams may be measuredfor nitrogenate content and/or the nitrogenate content thereof adjustedprior to the addition of the nitrogenate. Generally, a raw or untreatedfeed stream such as hydrocarbon feed stream 101 may contain some amountof oxygenate or nitrogenate when it enters the catalytic reaction systemdescribed herein. In addition, depending on the plant configuration, theduration of feed storage and weather conditions, the feed may absorboxygenates or nitrogenates from the air. In order to accurately controlthe amount of oxygenate or nitrogenates entering one or more of thearomatization reactors (e.g., reactors 10, 20, 30, 40), the amount ofoxygenate and/or nitrogenate in one or more feed streams to the reactorsmay be measured, adjusted, or both.

In an embodiment, the oxygenate and/or nitrogenate content of a givenstream such as a feed stream may be measured, for example with areal-time, in-line analyzer. In response to such measurement, theoxygenate and/or nitrogenate content of the stream may be adjusted bytreating and/or adding oxygenate and/or nitrogenate to the stream toobtain a desired amount of oxygenate and/or nitrogenate therein. In anembodiment, a control loop links the analyzer to a treater and anoxygenate and/or nitrogenate injector such that the amount of oxygenateand/or nitrogenate in one or more streams is controlled in response toan oxygenate and/or nitrogenate set point for such streams. In anembodiment the measuring and/or adjusting of the oxygenate and/ornitrogenate content and associated equipment such as treaters and/orchemical injectors are included as part of the purification process 80.The oxygenate and/or nitrogenate treaters vary based on the type andamounts of oxygenate and/or nitrogenate. In embodiments where theoxygenate comprises water, beds of sorbent materials may be used. Thesesorbent beds are commonly known as driers. In embodiments where theoxygenate comprises oxygen, the use of treaters which convert the oxygento water can be used in combination with driers. In further embodimentswhere the nitrogenate comprises a basic chemical, beds of sorbentmaterials may be used.

In an embodiment, one or more streams such as hydrocarbon feed 101,recycle stream 119, combined feed stream 102, hydrogen recycle 116, orcombinations thereof are treated prior to the addition of oxygenateand/or nitrogenate thereto. In such an embodiment, measuring theoxygenate and/or nitrogenate content of the streams before such treatedmay optionally be omitted. If there is no apparatus for readilymeasuring the oxygenate and/or nitrogenate content of the feed, then itis difficult to reliably maintain a desired level in the aromatizationreactors.

Treating one or more streams prior to the addition of the oxygenateand/or nitrogenate may aid in the overall control of the amount of waterand/or ammonia in one or more streams entering the aromatizationreactors by removing variability in the oxygenate and/or nitrogenatecontent in such streams. Treating such streams provides a consistent,baseline amount of oxygenate and/or nitrogenate in such streams for theaddition of oxygenate and/or nitrogenate to form an oxygenated streamsuch as reactor feed stream 106. When the reactor feed is sufficientlyfree of oxygenates and/or nitrogenates, precise quantities of theoxygenate and/or nitrogenates can be added to the reactor feeds suchthat the amount of oxygenate and/or nitrogenates in the reactors may bereliably maintained. In an embodiment, the purification process 80 mayinclude a hydrocarbon dryer that dries the hydrocarbon feed (e.g.,streams 101, 119, and/or 102) to a suitable water level. In otherembodiments, the purification process 80 may include a reduced copperbed (such as R3-15 catalyst available from BASF) or a bed of triethylaluminum on silica for use in removing oxygenates. In still furtherembodiments, the reduced copper bed (such as BASF R3-15 catalyst) or abed of triethyl aluminum on silica is used in combination with thehydrocarbon dryer. Similarly, the dryer 60 can be used to dry thehydrogen recycle and/or other process streams such as 101, 119, and/or102 to a suitable water level. In an embodiment a suitable oxygenatelevel in one or more streams such as hydrocarbon feed 101, recyclestream 119, combined feed stream 102, hydrogen recycle 116, is such thatthe combination thereof produces less than about 1 ppmv, alternativelyless than about 0.5 ppmv, or alternatively less than about 0.1 ppmv ofwater in the untreated hydrogen recycle stream 115. In an embodiment,one or more streams fed to the aromatization reactors such ashydrocarbon feed 101, recycle stream 119, combined feed stream 102,hydrogen recycle 116, or combinations thereof are substantially free ofwater following drying thereof. In an embodiment, the precise amount ofthe oxygenate and/or the nitrogenate may be added by partially or fullybypassing such treatment processes. Alternatively, the precise amount ofthe oxygenate and/or the nitrogenate may be added by partially or fullyrunning the hydrogen recycle stream through a wet, e.g. spent, molesieve bed.

In one embodiment, the amount of oxygenate added to the aromatizationprocess may be regulated to control the water content in the hydrogenrecycle stream 115. Specifically, the amount of oxygenate present in oneor more of the reactors 10, 20, 30, and 40 may be controlled by additionof the oxygenate as described and monitoring the amount of water exitingthe last reactor, for example the amount of water in effluent stream114, the hydrogen recycle 115 (upstream of dryer 60), or both. Having asufficient water level present in the hydrogen recycle 115 indicatesthat sufficient oxygenate is present in the reactors 10, 20, 30, and 40so that the catalyst is activated as described herein. However, thewater level in the hydrogen recycle stream 115 should also be limitedbecause excess water can decrease the useful life of the catalyst.Specifically, the upper limit of water addition should be determinedbased on the long-term catalyst activity. In various embodiments, theamount of oxygenate added to the catalytic reactor system 100 iscontrolled such that the hydrogen recycle stream 115 contains from about1 ppmv to about 100 ppmv, alternatively from about 1.5 ppmv to about 10ppmv, or alternatively from about 2 ppmv to about 4 ppmv of water. Inrelated embodiments, the amount of nitrogenate added to thearomatization process may be regulated to control the ammonia content inthe hydrogen recycle stream 115 in many of the same ways used for theoxygenate.

In another embodiment, the amount of oxygenate and/or nitrogenate addedto the aromatization process may be regulated to control the catalystactivity or to preserve the useful life of an aromatization catalyst.The catalyst activity can be measured by a number of methods includingthe endotherm, or ΔT, across one or more reactors or alternativelyT_(eq). Measurements of activity such as reactor temperature, inlettemperature, yield-adjusted temperature, fouling rate, etc. compareactivities at a given conversion of reactants in the reaction zone. Asused herein, the term “yield-adjusted temperature” or “T_(yld)” refersto the average catalyst bed temperature in a lab-scale reactor systemwhich has been adjusted to a specified yield (conversion) level. As usedherein, the term “T_(eq)” refers to the equivalent reactor weightedaverage inlet temperature (WAIT) that would be required to run acatalytic aromatization reaction to a specified conversion at a standardset of reactor operating conditions such as hydrocarbon feed rate,recycle hydrogen-to-hydrocarbon molar ratio, average reactor pressure,and concentration of feed-convertible components. T_(eq) can either beestablished by running at standard conditions or by using a suitablecorrelation to estimate T_(eq) based on measured values of reactorvariables. As used herein T_(eq) parameters include running thecatalytic aromatization reaction to about 88 wt % conversion of C₆convertibles at a hydrogen-to-hydrocarbon ratio of about 4.0, a spacevelocity of about 1.2 hr⁻¹, in a six adiabatic reactor train with theinlet pressure to the last reactor at about 50 psig, with a feedcomposition comprising a C₆ fraction greater or equal to 90 wt %; a C₅fraction less than or equal to 5 wt %; and a C₇ ⁺ fraction less than orequal to 5 wt %. As used herein, the conversion of C₆ convertiblesrefers to the conversion of C₆ molecules with one or fewer branches intoaromatic compounds. In various embodiments, the amount of oxygenateand/or nitrogenate added to the catalytic reactor system 100 isregulated such that the T_(eq) is from about 900° F. to about 1000° F.,from about 910° F. to about 960° F., or from about 920° F. to about 940°F. Furthermore, because any increase in catalyst activity is evidencedby a decrease in T_(eq), the increase in catalyst activity can also bemeasured as a percentage decrease in the T_(eq) of an equivalent reactorsystem running an equivalent dry hydrocarbon feed. In variousembodiments, the amount of oxygenate added to the catalytic reactorsystem 100 is controlled such that the T_(eq) is from about 0 percent toabout 25 percent, alternatively from about 0.1 percent to about 10percent, or alternatively from about 1 percent to about 5 percent lessthan the T_(eq) of an equivalent reactor system running an equivalentsubstantially dry hydrocarbon feed, for example resulting in less thanabout 1 ppmv water in the hydrogen recycle stream 115, alternativelyless than about 0.5 ppmv total water. In related embodiments, the amountof nitrogenate added to the aromatization process may be regulated tocontrol the catalyst activity in many of the same ways used for theoxygenate.

Furthermore, the use of the oxygenate and/or nitrogenate in thecatalytic reactor system may have a beneficial effect on the foulingrate of the catalyst. Catalysts may have a useful life beyond which itis no longer economically advantageous to use the catalyst. Acommercially valuable catalyst will exhibit a relatively low and stablefouling rate. It is contemplated that the use of the oxygenate and/ornitrogenate as described herein increases and maintains the potentiallife of the catalyst when operating under conditions substantially freeof these chemicals, for example, containing less than about 1 ppmv totaloxygenate in stream 107 alternatively less than about 0.5 ppmv totaloxygenate in stream 107.

Various types of catalysts may be used with the catalytic reactor systemdescribed herein. In an embodiment, the catalyst is a non-acidiccatalyst that comprises a non-acidic zeolite support, a group VIIImetal, and one or more halides. Suitable halides include chloride,fluoride, bromide, iodide, or combinations thereof. Suitable Group VIIImetals include iron, cobalt, nickel, ruthenium, rhodium, palladium,osmium, iridium, and platinum. Examples of catalysts suitable for usewith the catalytic reactor system described herein are the AROMAX® brandof catalysts available from the Chevron Phillips Chemical Company of TheWoodlands, Texas, and those discussed in U.S. Pat. No. 6,812,180 toFukunaga entitled “Method for Preparing Catalyst”, and U.S. Pat. No.7,153,801 to Wu entitled “Aromatization Catalyst and Methods of Makingand Using Same”, each of which is incorporated herein by reference as ifreproduced in their entirety.

Supports for aromatization catalysts can generally include any inorganicoxide. These inorganic oxides include bound large pore aluminosilicates(zeolites), amorphous inorganic oxides and mixtures thereof. Large porealuminosilicates include, but are not limited to, L-zeolite, Y-zeolite,mordenite, omega zeolite, beta zeolite and the like. Amorphous inorganicoxides include, but are not limited to, aluminum oxide, silicon oxide,and titania. Suitable bonding agents for the inorganic oxides include,but are not limited to, silica, alumina, clays, titania, and magnesiumoxide.

Zeolite materials, both natural and synthetic, are known to havecatalytic properties for many hydrocarbon processes. Zeolites typicallyare ordered porous crystalline aluminosilicates having structure withcavities and channels interconnected by channels. The cavities andchannels throughout the crystalline material generally can be of a sizeto allow selective separation of hydrocarbons.

The term “zeolite” generally refers to a particular group of hydrated,crystalline metal aluminosilicates. These zeolites exhibit a network ofSiO₄ and AlO₄ tetrahedra in which aluminum and silicon atoms arecrosslinked in a three-dimensional framework by sharing oxygen atoms. Inthe framework, the ratio of oxygen atoms to the total of aluminum andsilicon atoms may be equal to 2. The framework exhibits a negativeelectrovalence that typically is balanced by the inclusion of cationswithin the crystal such as metals, alkali metals, alkaline earth metals,or hydrogen.

L-type zeolite catalysts are a sub-group of zeolitic catalysts. TypicalL-type zeolites contain mole ratios of oxides in accordance with thefollowing formula:

M_(2/n)O.Al₂O₃.xSiO₂.yH₂O

wherein “M” designates at least one exchangeable cation such as barium,calcium, cerium, lithium, magnesium, potassium, sodium, strontium, andzinc as well as non-metallic cations like hydronium and ammonium ionswhich may be replaced by other exchangeable cations without causing asubstantial alteration of the basic crystal structure of the L-typezeolite. The “n” in the formula represents the valence of “M”, “x” is 2or greater; and “y” is the number of water molecules contained in thechannels or interconnected voids with the zeolite.

Bound potassium L-type zeolites, or KL zeolites, have been found to beparticularly desirable. The term “KL zeolite” as used herein refers toL-type zeolites in which the principal cation M incorporated in thezeolite is potassium. A KL zeolite may be cation-exchanged orimpregnated with another metal and one or more halides to produce aplatinum-impregnated, halided zeolite or a KL supported Pt-halidezeolite catalyst.

In an embodiment, the Group VIII metal is platinum. The platinum andoptionally one or more halides may be added to the zeolite support byany suitable method, for example via impregnation with a solution of aplatinum-containing compound and one or more halide-containingcompounds. For example, the platinum-containing compound can be anydecomposable platinum-containing compound. Examples of such compoundsinclude, but are not limited to, ammonium tetrachloroplatinate,chloroplatinic acid, diammineplatinum (II) nitrite,bis-(ethylenediamine)platinum (II) chloride, platinum (II)acetylacetonate, dichlorodiammine platinum, platinum (II) chloride,tetraammineplatinum (II) hydroxide, tetraammineplatinum chloride, andtetraammineplatinum (II) nitrate.

In an embodiment, the catalyst is a large pore zeolite support with aplatinum-containing compound and at least one organic ammonium halidecompound. The organic ammonium halide compound may comprise one or morecompounds represented by the formula N(R)₄X, where X is a halide andwhere R represents a hydrogen or a substituted or unsubstituted carbonchain molecule having 1-20 carbons wherein each R may be the same ordifferent. In an embodiment, R is selected from the group consisting ofmethyl, ethyl, propyl, butyl, and combinations thereof, morespecifically methyl. Examples of suitable organic ammonium compound isrepresented by the formula N(R)₄X include ammonium chloride, ammoniumfluoride, and tetraalkylammonium halides such as tetramethylammoniumchloride, tetramethylammonium fluoride, tetraethylammonium chloride,tetraethylammonium fluoride, tetrapropylammonium chloride,tetrapropylammonium fluoride, tetrabutylammonium chloride,tetrabutylammonium fluoride, methyltriethylammonium chloride,methyltriethylammonium fluoride, and combinations thereof.

In an embodiment, the organic ammonium halide compound comprises atleast one acid halide and at least one ammonium hydroxide represented bythe formula N(R′)₄OH, where R′ is hydrogen or a substituted orunsubstituted carbon chain molecule having 1-20 carbon atoms whereineach R′ may be the same or different. In an embodiment, R′ is selectedfrom the group consisting of methyl, ethyl, propyl, butyl, andcombinations thereof, more specifically methyl. Examples of suitableammonium hydroxide represented by the formula N(R′)₄OH include ammoniumhydroxide, tetraalkylammonium hydroxides such as tetramethylammoniumhydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide,tetrabutylammonium hydroxide, and combinations thereof. Examples ofsuitable acid halides include HCl, HF, HBr, HI, or combinations thereof.

In an embodiment the organic ammonium halide compound comprises (a) acompound represented by the formula N(R)₄X, where X is a halide andwhere R represents a hydrogen or a substituted or unsubstituted carbonchain molecule having 1-20 carbons wherein each R may be the same ordifferent and (b) at least one acid halide and at least one ammoniumhydroxide represented by the formula N(R′)₄OH, where R′ is hydrogen or asubstituted or unsubstituted carbon chain molecule having 1-20 carbonatoms wherein each R′ may be the same or different.

The halide-containing compound may further comprise an ammonium halidesuch as ammonium chloride, ammonium fluoride, or both in variouscombinations with the organic ammonium halide compounds describedpreviously. More specifically, ammonium chloride, ammonium fluoride, orboth may be used with (a) as described previously, a compoundrepresented by the formula N(R)₄X, where X is a halide and where Rrepresents a hydrogen or a substituted or unsubstituted carbon chainmolecule having 1-20 carbons wherein each R may be the same or differentand/or (b) as described previously, at least one acid halide and atleast one organic ammonium hydroxide represented by the formulaN(R′)₄OH, where R′ is a substituted or unsubstituted carbon chainmolecule having 1-20 carbon atoms wherein each R′ may be the same ordifferent. For example, a first fluoride- or chloride-containingcompound can be introduced as a tetraalkylammonium halide with a secondfluoride- or chloride-containing compound introduced as an ammoniumhalide. In an embodiment, tetraalkylammonium chloride is used withammonium fluoride.

EXAMPLES

Having described the methods for activating and enhancing thearomatization catalyst with an oxygenate and/or nitrogenate andcontrolling the amounts thereof by monitoring process parameters, thefollowing examples are given as particular embodiments of the methoddisclosed and to demonstrate the practice and advantages thereof. Forthe following examples, water or oxygen was injected into thearomatization feed prior to the first reactor as shown in FIG. 1 anddescribed herein, unless otherwise described in the examples. It isunderstood that the examples are given by way of illustration and arenot intended to limit the specification or the claims to follow in anymanner.

Example 1

In a first example, the water in the recycle hydrogen was maintainedbelow about 1 ppmv. The experiment was conducted in a series of 6adiabatic reactors operating at a liquid hourly space velocity of about0.8 to about 1.2 hr⁻¹, a hydrogen-to-hydrocarbon ratio of about 3 toabout 6, and a sixth reactor inlet pressure of about 50 psig. Eachindividual reactor was a radial flow reactor with an internal diameterof between about 3 and about 10 feet. The feed was treated prior to usesuch that less than about 1.0 ppmv of oxygenates were present. Thus,this configuration does not contain any added oxygenate and/ornitrogenate and can be used as a reference.

Example 2

The process of example 1 was repeated except that the water in therecycle hydrogen was varied from about 2 to about 9 ppmv through theaddition of water to streams 107 or 109 of FIG. 1. FIGS. 3A and 3Billustrate the effect that the presence of water as an oxygenate has onthe T_(eq) for the catalyst activity in examples 1 and 2. Specifically,FIG. 3A depicts the amount of water present in parts per million in thehydrogen recycle gas stream 115 for example 1 and example 2, whereasFIG. 3B depicts the T_(eq) in degrees Fahrenheit for the same twoexamples. The hollow diamonds in FIGS. 3A and 3B are data from Example1, run under substantially dry conditions, that is without the additionof any water to the system. The solid squares in FIGS. 3A and 3B aredata from Example 2, the experiment in which the oxygenate was added tothe system prior to the first aromatization reactor. As can be seen inFIGS. 3A and 3B, when the system was run under substantially dryconditions, the catalyst activity continually decreased, as representedby a continuous increase in T_(eq) for the aromatization reactors. Incontrast, when the same process used the same catalyst but with theaddition of the oxygenate prior to the first aromatization reactor, thecatalyst maintained its high initial activity as represented by the lowand relatively constant T_(eq) shown at the bottom of FIG. 3B.

The relationship between the water content of the hydrogen recyclestream and the catalyst activity may also be reversible. On about day 6of the oxygenated run (Example 2) the addition of water to the systemceased, as shown by the reduced water in the hydrogen recycle on FIG.3A. Starting at day 6, the catalyst activity decreased as evidenced bythe increased T_(eq) shown in FIG. 3B. By about day 10, the amount ofwater in the hydrogen recycle was about 2 ppmv, a level approaching thelevels seen at the beginning of the substantially dry run, about 1.5ppmv. When the addition of oxygenate resumed on day 10, the catalystactivity returned to its previous levels as evidenced by the decreasedT_(eq) shown in FIG. 3B. This increase and decrease in T_(eq) forms aslight hump in the graph for Example 2 at the bottom of FIG. 3B betweendays 6 and 12.

Example 3

The relationship between the water content of the hydrogen recyclestream and the catalyst activity may also be catalyst specific as shownin this example. An experiment was conducted to determine the short-termaffect of oxygenate addition on aromatization catalyst activity for twodifferent catalyst formulations. The first catalyst was comprised ofL-zeolite, impregnated with platinum, which had not been furtherimpregnated with the halogens chloride, and fluoride (Pt/L-zeolite). Thesecond catalyst was comprised of L-zeolite, impregnated with platinum,along with the halogens chloride, and fluoride (Pt/Cl/F/L-zeolite). Inthis example, the two catalysts were first brought to stable operatingconditions without the addition of an oxygenate at about 3.0 liquidhourly space velocity (LHSV); about 140 psig; about 3.0 H₂/hydrocarbonfeed ratio; at a temperature that achieved a significant aromatic yield.Once stable operations had been established the processes were thenperturbed by the addition of equal amounts of oxygenate, specifically atrace amount of O₂ in the hydrogen feed, for a period of about 24 hours.The oxygenate addition was measured as water in the off-gas from thereactor. During these short-term perturbation tests, the catalyst bedtemperatures were held constant. The response of the catalyst activityto the addition of oxygenate, and the subsequent cessation of oxygenateaddition, was measured using the T_(ym).

As shown by the steady plot for T_(yld) in FIG. 4, the presence of theoxygenate did not have an affect on the activity of the Pt/L-zeolitecatalyst. Similarly, the removal of the oxygenate did not have an affecton the activity of the Pt/L-zeolite catalyst either, as the plot ofT_(yld) in FIG. 4 remained steady before, during, and after theoxygenate injection. In contrast, FIG. 5 shows that the addition of theoxygenate increased the activity of the Pt/Cl/F/L-zeolite catalyst, asevidenced by the decrease in the T_(yld) for the aromatization reactorduring the interval of oxygenate injection. Moreover, when the oxygenateaddition was terminated, the T_(yld) returned to its previous, higherlevels. As noted previously, for an endothermic aromatization reactionas carried out in the Examples, a higher T_(yld) is associated with alower catalyst activity and vice-versa.

Example 4

This example further exemplifies of the use of oxygenates to improve andcontrol catalyst activity. In this example a feed of having a C₆concentration of less than or equal to about 63 wt %; a C₅ concentrationof less than or equal to about 5 wt %; a C₇ concentration of less thanor equal to about 27 wt % C₇; and a C₈ ⁺ concentration of less than orequal to about 10 wt % was fed to a single reactor. The single reactorwas operating at a pressure of about 65 psig, with ahydrogen-to-hydrocarbon molar ratio of about 2.0 and a liquid hourlyspace velocity of about 1.6 hr⁻¹. The downflow reactor was a packed bedreactor with an internal diameter of about 1.0 inch. The feed waspretreated using a combination of Type 4A molecular sieves and reducedBASF-R3-15 (40 wt % copper) to less than about 1.0 ppmv oxygenate.During the run of this example, the amount of oxygenate in the reactorfeed was varied by adjusting the flow rate of O₂ in a carrier gas ofhydrogen being injected into the feed stream. The results of thisexample are presented in FIG. 6. As shown, the substantial variation inT_(yld) corresponds to variations in the measured water in the recyclehydrogen stream.

Example 5

This experiment illustrates the effect that water has on the life of anaromatization catalyst. In this example, two side-by-side laboratoryscale isothermal reforming reactor systems were started under the sameprocess conditions, both using the same halogenated Pt/K-L zeolitecatalyst. Both reactors exhibited the typical spike in water (measuredin the reactor product gas) during the initial 4 to 6 hours ofoperation, which subsequently decayed for the remainder of the 50 hourlow severity “break-in.” Low severity conditions were 3.0 LHSV, 3.0H₂/hydrocarbon, 140 psig, with 60% aromatics in the liquid product. At50 hours on stream (HOS), both reactors were set to high severity. Highseverity conditions were 3.0 LHSV, 0.5 H₂/hydrocarbon, 140 psig, with76% aromatics in the liquid product. Both reactors exhibited the typicalspike in water in transition to high severity, which subsequentlydecayed. For the first 100 HOS, both reactors were subject to the sameexperimental conditions and both reactors had comparable performance.

Run 1 was continued from 50 to about 1600 HOS without the addition ofwater, e.g. was run substantially dry. Run 1 leveled off at about 2 ppmvof water in the off-gas by about 500 HOS. The water level in Run 1stayed at about 2 ppmv through about 1600 HOS. In contrast, water wasadded to Run 2, the substantially wet run. Specifically, at 100 HOS thewater level was increased in the second reactor, e.g. the reactorassociated with Run 2, via controlled addition of trace oxygen in thehydrogen feed. The Run 2 moisture level reached about 8 ppmv water by500 HOS, where it stayed through about 1600 HOS.

In this example, the Start of Run (SOR) yield-adjusted reactortemperatures for both Run 1 and Run 2 were about 940° F. The End of Run(EOR) temperature for this example was defined as 1000° F. At about 1600HOS, the yield-adjusted reactor temperature for both runs is about 985to 990° F., and thus both runs are approaching the EOR temperature.Consequently, at about 1600 HOS the water level in both Run 1 and Run 2was increased by about 5 to 6 ppmv water, so that the Run 1 reactoroff-gas increased to about 8 ppmv water and the Run 2 reactor off-gasincreased to about 13.5 ppmv water. The Run 2 reactor continued todeactivate at the same rate. That is the increase from 8 to 13.5 ppmvwater did not change the fouling rate or the catalyst activity. Incontrast, the catalyst activity in the Run 1 reactor increasedsubstantially when the water in the off-gas changed from 2 to 8 ppmv, asseen by the decrease in the reactor yield-adjusted temperature from1600-1750 HOS. At about 1750 HOS, the Run 1 reactor activity began todecay again, but at a lower decay rate than prior to the water increase.

FIG. 7 illustrates the results of this example. No data is plottedduring the first about 50 HOS of FIG. 7 which represents the start-upperiod in which the reactors are operated under non-standard operatingconditions. Run 1 was used to predict point A and determine point C,whereas Run 2 was used to determine point B. The substantially dry run,Run 1, is predicted to reach EOR at point A. The substantially wet run,Run 2, which had about 8 ppmv of water for most of the run, had an EORat about point B. However, the best run length is achieved by operatingat moderately-low water (e.g. 2 ppmv) through most of the cycle and thenadding water to the feed to achieve 8 ppmv water in the off-gas justprior to reaching the EOR temperature. This approach is better than thetwo previous, and results in endpoint C. The difference between points Aand B is about 200 hours, which is an increase of about 10% over pointA, and the difference between points B and C is about 200 hours. Thus, alate addition of water to the catalyst system can result in about 400more hours of useful catalyst life, which is an increase of about 20%over the dry run.

Example 6

An experiment was conducted on a full-scale reactor system similar tothe one described in FIG. 1. Specifically, the aromatization process wasrun under normal conditions to develop a baseline for the trial. FIGS.8A-8D illustrate the reactor history and performance.

On day 623, water injection was started at stream 107 in FIG. 1 at arate of 12 milliliters per minute to produce an estimated water contentin the recycle gas of 5 ppmv. The water content in the recycle gasstream (stream 115 in FIG. 1) increased from 1.2 ppmv to 4 ppmv. On day624, an increase in catalyst activity was observed, and the WAIT wasdecreased by 1.5° C. to 530° C., and the reactor space velocity (hr⁻¹)was increased by 0.75%. On day 625, the water injection rate was reducedfrom 12 ml/min to 6 ml/min to control catalyst activity increase and toimprove H₂ production purity. The WAIT was decreased from 529° C. to528.5° C., and the reactor was maintained at the higher space velocity.After day 626, the catalyst activity was expected to follow the activitydecay of the previous catalyst charge, thus yielding an estimatedadditional about 150 days on stream. Table 1 shows the results:

TABLE 1 Days on Stream 588 595 602 616 623 624 625 626 WAIT, ° C. 529530 530.5 527 531.5 531.5 530 529 Benzene 47.4 47.7 48 47.4 47.1 48.648.9 47.8 Yield, Wt % Toluene 16.2 16.3 15.5 15.3 15.7 15.3 15.1 15.1Yield, Wt % C₆ Precursor 87.4 88 88 86.3 87.7 90.7 90.8 89.5 Conversion,% C₆ Precursor 89.4 86.7 87.2 87.1 85.4 86.5 87.7 85.9 Selectivity toBenzene, Wt % Total 399.4 398.7 396.9 388 395.8 392.9 388.5 385.3Endotherm, ° C. Teq, ° C. 528.6 528.3 528.3 528.6 528.7 525.4 523.6523.9

Example 7

The results reported in examples 7 and 8 were obtained usingexperimental units such as those described in examples 5 and 6 of U.S.Pat. No. 6,190,539 to Holtermann and entitled “Reforming using a boundhalided zeolite catalyst.” In this example and the following example,the experimental equipment was routinely operated with less than 1 ppmvH₂O in the recycle hydrogen. The experimental equipment was modified sothat oxygen could be added to the recycle hydrogen stream. This oxygenwas then converted to water as it passed through the catalyst within thehydrofining section. The oxygen addition was then controlled bymeasuring the water level in the recycle hydrogen. In this example,oxygen was injected into the recycle and the resulting yield-adjustedcatalyst average temperature was plotted in FIG. 9. Furnace temperaturewas held constant and changes in catalyst activity were monitored bymeasuring changes in the yield-adjusted catalyst temperature.Specifically, about 400 ppmv of O₂ in H₂ was added at a rate of 0.08cubic centimeters per minute per gram of catalyst (cc/min·g_(catalyst))starting about 14,100 hours. The oxygen addition rate was increased toabout 0.17 cc/min·g_(catalyst) at about 14,300 hours, and oxygenaddition ended at about 14,800 hours. Linear regression of thetemperature before injection, during injection, and after injection wasconducted for the temperature values. As shown, the slope was lowerduring O₂ injection, indicating a lower deactivation rate during O₂injection, compared to before and after the O₂ injection. Specifically,the fouling rate of the catalyst before the water addition was 0.13°F./day. The fouling rate of the catalyst during the water addition was0.05° F./day. Finally, the fouling rate of the catalyst after the wateraddition was 0.28° F./day.

Example 8

In this example, furnace temperature was again held steady so thatreactor endotherms could be monitored precisely with time and watercontent. This run operated at 65 psig, 1.6 LHSV, 2.0 H₂/hydrocarbon moleratio.

From the outset, there was low water concentrations (<2 ppmv, withlevels reaching <1 ppmv at times) in the recycle hydrogen and the resultwas decreasing catalyst activity almost immediately following theextended reactor idle time at about 500 HOS. As shown in FIG. 10, whenwater was added to the reactor system via oxygen addition to the recyclegas at 1,600 HOS and activity was restored. When water addition to thearomatization reactor was stopped, the activity decayed once again inthe period between 2,000 and 3,100 HOS. Subsequently, increasing waterlevels via oxygen addition caused an increase in the catalyst activityup to about 4 or 5 ppmv water. Further increases in water did not raiseactivity further. When water addition was stopped at 3,900 HOS, catalystactivity started to fall again immediately.

The oxygen (O₂) addition was initiated upstream of the hydrofiningsystem at 3,900 HOS. The reaction rate in the aromatization reactorstarted to increase in a (top down) wave through the reactor about 11hours prior to the detection of increased water in the effluent hydrogenfrom aromatization reactor at 1,650 HOS. The increased reaction rate isindicated by the increase in the reactor endotherm (reduction inthermowell temperatures by as much as 10° F.). In FIG. 11, the internalthermowell temperatures during the run are plotted between 1,600 and1,700 HOS during the time period of the first oxygen addition. It can beseen (in FIG. 11) that the reactor internal temperatures started to move(temperatures decreased, which indicates an increase in the reactorendotherm, and catalyst activity) about 11 hours prior to detection ofwater in the reactor outlet.

During periods of low moisture operation, only the conversion to benzenewas adversely affected. The conversions to toluene and xylenes remainedinvariant. This behavior is illustrated in FIG. 10. When moisture levelswere increase via oxygen addition at about 1,600 HOS, the benzeneconcentration in the effluent increase about 8% from 40% to 48%.

While preferred embodiments of the disclosure have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the disclosure. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the disclosuredisclosed herein are possible and are within the scope of thedisclosure. Where numerical ranges or limitations are expressly stated,such express ranges or limitations should be understood to includeiterative ranges or limitations of like magnitude falling within theexpressly stated ranges or limitations (e.g., from about 1 to about 10includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13,etc.). Use of the term “optionally” with respect to any element of aclaim is intended to mean that the subject element is required, oralternatively, is not required. Both alternatives are intended to bewithin the scope of the claim. Use of broader terms such as comprises,includes, having, etc. should be understood to provide support fornarrower terms such as consisting of, consisting essentially of,comprised substantially of, etc.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present disclosure. Thus, the claims are a further description andare an addition to the preferred embodiments of the present disclosure.The discussion of a reference herein is not an admission that it isprior art to the present disclosure, especially any reference that mayhave a publication date after the priority date of this application. Thedisclosures of all patents, patent applications, and publications citedherein are hereby incorporated by reference, to the extent that theyprovide exemplary, procedural, or other details supplementary to thoseset forth herein.

1. A hydrocarbon aromatization process comprising: adding a nitrogenateto a hydrocarbon stream to produce an enhanced hydrocarbon stream;contacting the enhanced hydrocarbon stream with an aromatizationcatalyst in a reaction zone; and recovering an effluent comprisingaromatic hydrocarbons.
 2. The process of claim 1 further comprisingseparating a hydrogen recycle stream from the effluent, wherein thehydrogen recycle stream has a water content of from about 1 ppmv toabout 100 ppmv.
 3. The process of claim 2 further comprising drying thehydrogen recycle stream to produce a dried hydrogen recycle streamhaving a water content of less than about 1 ppmv and feeding the driedhydrogen recycle stream to the hydrocarbon stream or the enhancedhydrocarbon stream.
 4. The process of claim 1 further comprisingcontrolling the addition of the nitrogenate to the hydrocarbon stream tomaintain one or more process parameters within a desired range.
 5. Theprocess of claim 1 further comprising controlling the addition of thenitrogenate to the hydrocarbon stream to increase the production of oneor more aromatic compounds in the reaction zone effluent by at leastabout 1 percent over pre-addition levels.
 6. The process of claim 1further comprising controlling the addition of the nitrogenate to thehydrocarbon stream to increase the catalyst selectivity to benzene inthe reaction zone effluent by at least about 1 percent over pre-additionlevels.
 7. The process of claim 1 further comprising prior to theaddition of the nitrogenate, treating the hydrocarbon stream to removeall or a portion of any nitrogenates, oxygenates, or both therein toproduce a treated hydrocarbon stream.
 8. The process of claim 7 whereinthe oxygenate removed from the hydrocarbon stream comprises water, andwherein the treated hydrocarbon stream has a water content of less thanabout 1 ppmv.
 9. The process of claim 1 wherein the aromatizationprocess comprises a plurality of reactors, and the nitrogenate is addedto one or more of the reactors.
 10. The process of claim 1 wherein thenitrogenate comprises ammonia or one or more ammonia precursors thatform ammonia in the reaction zone.
 11. The process of claim 1 whereinthe aromatization catalyst comprises a non-acidic zeolite support, agroup VIII metal, and one or more halides.
 12. The process of claim 11wherein the non-acidic zeolite support is zeolite L, zeolite X, zeoliteY, zeolite omega, beta, mordenite, or combinations thereof, the GroupVIII metal is platinum, and the one or more halides are fluoride,chloride, bromide, iodide, or combinations thereof.
 13. The process ofclaim 1 wherein the oxygenate is used in combination with a nitrogenate.14. A hydrocarbon aromatization process comprising: adding a nitrogenateto a hydrocarbon stream to produce an enhanced hydrocarbon stream, to ahydrogen recycle stream to produce an enhanced recycle stream, or toboth; contacting the enhanced recycle stream, alone or in combinationwith the enhanced hydrocarbon stream with an aromatization catalyst;recovering an effluent comprising aromatic hydrocarbons; and controllingthe addition of the nitrogenate to the hydrocarbon stream, the recyclestream, or both in order to maintain one or more process parameterswithin a desired range.
 15. The process of claim 14 wherein thenitrogenate is controlled to maintain a T_(eq) across one or morereactors in the process.
 16. The process of claim 15 wherein the T_(eq)in the one or more reactors is decreased in comparison to a T_(eq) thatoccurs in the absence of the nitrogenate.
 17. The process of claim 14wherein the T_(eq) decreases from about 0.1 percent to about 25 percent.18. The process of claim 14 wherein the nitrogenate is used incombination with an oxygenate.
 19. A hydrocarbon aromatization processcomprising: monitoring the presence of a nitrogenate in thearomatization process; monitoring at least one parameter of thearomatization process that indicates the activity of an aromatizationcatalyst; and modifying the amount of the nitrogenate in thearomatization process, thereby affecting the parameter.
 20. The processof claim 19 wherein the parameter is benzene production, and whereinupon the modification of the amount of the nitrogenate in thearomatization process, benzene production is increased by at least about1 percent as compared to the benzene production prior to modifying theamount of the nitrogenate.
 21. The process of claim 19 wherein theparameter is a useful life of the aromatization catalyst, and whereinthe useful life of the aromatization catalyst is increased by at leastabout 5 percent as compared to a similar catalyst in which the amount ofthe nitrogenate has not been modified.
 22. The process of claim 19wherein the modification comprises increasing an amount of thenitrogenate in the aromatization process to a first level, thendecreasing the amount of the nitrogenate in the aromatization process toa second level.
 23. The process of claim 22 wherein the parameter is auseful life of the aromatization catalyst, and wherein the modificationincreases the useful life of the aromatization catalyst as compared toeither a first similar aromatization catalyst in which the amount of thenitrogenate is maintained at the first level or a second similararomatization catalyst in which the amount of the nitrogenate ismaintained at the second level.